Mechanisms of 2,4,6-trichlorophenol removal by activated persulfate with hexagonal Fe7S8 sheets and enhancing removal by oxidizing porous media

Pyrrhotite (Fe 7 S 8 ) is a natural mineral with multiple valence states of iron and an efficient peroxydisulfate (PS) activator. However, the activation mechanism of PS and the performance of 2,4,6-trichlorophenol (TCP) removal by the Fe 7 S 8 /PS system are not clear. Herein, the hexagonal Fe 7 S 8 sheets were fabricated using the facile one-step solvothermal method, which could enhance PS activation and TCP degradation. The Fe 7 S 8 /PS system removed 94.3% of the TCP within 60 min with an apparent rate constant of 0.052 ± 0.003 min −1 . The dissolution of Fe 7 S 8 during the Fe 7 S 8 /PS activation facilitated the regeneration of Fe 3+ /Fe 2+ redox cycles. Free radical species analysis confirmed the presence of sulfate radical (SO 4 •- ) and hydroxyl radical (•OH). The fundamental involvement of the free radicals was observed in two stages. The first stage (0–5 min) was dominated by the contribution of •OH, whereas, in 2nd stage (5–60 min), the contribution of SO 4 •- exceeded that of •OH. Toxicity prediction studies revealed that degradation intermediates had lower toxicity than TCP. In the reaction column filled with 15 g of quartz sand (QS), the removal efficiency on TCP decreased from 100% to 0% over a period of 30 min to 80 h. In addition, after 155 h, the TCP removal efficiencies of column experiments loaded with 15, 18, and 20 g of QS and Fe 7 S 8 were 33.2%, 44.6%, and 50.2%, respectively. These findings suggested the Fe 7 S 8 /PS system showed high potential for removing TCP from groundwater.